The present invention relates to a device for measuring the relative efficiency of operation of a heat pump.
It is a basic principle of the operation of a heat pump that its heat output, and therefore the air temperature rise across its indoor condensor coil, drops as the outdoor temperature drops. As a result, below certain outdoor temperatures, supplemental heaters are ordinarily required to operate along with a heat pump in order to maintain a space being heated at a given temperature. Such supplemental heaters are normally activated to maintain the indoor temperature at a particular level by a mechanism, such as a thermostat, which is independent of the heat pump's operation. If a malfunction in the heat pump should occur, resulting in a reduction in its heat output, the supplemental heaters will be activated to maintain the desired indoor temperature and this will result in unnecessary expense in operating the supplemental heaters.
In order to minimize this expense and prevent heat pump malfunctions from worsening, it is therefore important that all heat pump malfunctions be quickly and easily detected. However, several features of heat pump systems including those discussed above, present a problem in detecting malfunctions of a heat pump. For example, a malfunction cannot be detected merely by observing the room temperature. Nor can a malfunction be detected by observing the output of the heat pump or the operation of the supplemental heater alone, without consideration of the outdoor temperature, since the latter significantly influences the heat pump system output. Furthermore, heat pumps are known to experience several types malfunctions and therefore monitoring only one or two of them will not alert those concerned to all of the various defects or failures which could lower the heat pump output. Such other failures which could cause reduced heat output include, for example, partial loss of refrigerant, malfunction of the indoor and outdoor coil refrigerant feed device, failure of system or control power, and blockage of the outdoor coil by debris.
Previous attempts to monitor the operation of a heat pump have been directed to the detection of particular malfunctions of the heat pump. For example, U.S. Pat. No. 2,054,542 (Hoelle, 1936) discloses a device which indicates abnormal operation of a compressor in a refrigerating machine. U.S. Pat. No. 3,628,346 (Lagrone, 1967) discloses a device for indicating a malfunction in the fan or motor-compressor of a central air conditioning system. However, as indicated above, such devices do not indicate whether some other defect or failure may be causing a reduction in heat pump output.
Other patents show automatic control of heat pump systems and air conditioning systems. For example, U.S. Pat. No. 3,381,489 (Biehn, 1968) shows the use of a thermistor, responsive to the temperature of the outdoor coil of a heat pump, for adjusting the speed of the motor of the fan used for moving outdoor air over the surface of the outdoor coil. U.S. Pat. No. 3,058,724 (Maudlin, 1962) and U.S. Pat. No. 2,672,734 (Ditzler, 1954) disclose heat pump apparatuses which control and indicate the use of auxiliary heaters. However, as indicated above, even with the use of automatic devices for indicating and controlling on supplemental heat, a separate determination must be made as to whether supplemental heat is required at a particular time or whether the heat pump is operating inefficiently.